I'm planning to have our consumer unit modernized and upgraded (by a professional) in the near future: one big one with RCBOs to replace the Henley block and two old ones (one with a general RCD, one without).
What measure can I take to minimize the amount of fuss that will ensue as part of the upgrade?
I would like to have three double sockets in the house either RCD-free or with RCD sockets and no upstream RCD/RCBO in order to reduce the harm from nuisance trips. These would supply the fridge and freezer in the cellar, the fridge-freezer in the dining room, and the "network cabinet" in the back of a wardrobe on the first floor.
What hoops do I need to jump through to get these? (In all three cases I can get the wiring from the the CU in the cellar to the socket without burying any cable in plaster.)
This comes up so often. In a domestic environment, and that includes all outbuildings, all sockets MUST be RCD protected.
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and somewhere some one makes the observation:-
"This is a no brainer. A metal cased fridge is put into a damp cellar. The metal gets touched regularly during use. It will get really wet when being defrosted. RCD / RCBO is the only way to go."
&
"Their is no question, the regulations are very clear and unambiguous, the circuit needs protection if a RCcD is not to be used then a RCBO must be. To provide the circuit with neither would contravene the regulations rendering the installer liable if something goes wrong, would the client prefer a fault to cause a fire?"
So the gist of the OP's question is "how do you get a circuit which bypasses the house RCD and feeds sockets which have their own RCD?". So all sockets are still protected by RCD, but not necessarily the *same* one.
Better to have a separate RCD for the always-on devices different to the one used for all other devices. That way, a fault elsewhere in the house does not trip the critical devices, and only a fault in a critical device will trip its own RCD.
Sadly most house installations have a single RCD that covers the whole house, so a fault with a non-critical device will take out even the critical devices.
At our last house we had a supply to an outhouse, used for sockets for the lawnmower and (in the early days) a freezer (*). We found out by bitter experience that even with nothing plugged into any sockets in the outhouse, the RCD would trip if there was a thunderstorm in the area. We lost a freezer-load of food when this happened while we were away on holiday.
After that we got into the habit of always turning of the MCB to the outhouse circuit whenever we went away on holiday. That prevented the RCD tripping. If the RCD did trip for any other reason, it was usually triggered by something we did so we'd be around the reset it after resolving the cause. We didn't lose any more frozen food after that. An alarm is only any good if there's someone around to hear it and to try resetting the RCD ;-)
(*) We stopped using a freezer in the outhouse after it started to warm up in very cold weather because we'd gone outside the permitted range of ambient temperatures. That was when we learned that Beko are one of the few manufacturers whose freezers (but not fridge/freezers) can be used down to about -15 deg C, so we bought a Beko replacement in case at any stage in the future we might want to put it outside.
If the O/P wants maximum independence of the three fridge, freezer and networking sockets, then plan to give each of them its own radial circuit on its own RCBO in the new CU. Pending the install of the new CU maybe connect them as spurs off the ring?
If the OP used armoured cable or sunk under plaster a sufficient distance etc, would he not be able to use a fixed outlet without RCD protection?
My preference with such a concern would be to have a dedicated circuit with RCBO protection at the CU. And to perhaps have an audible alarm if the temperature should rise above some chosen value.
while discussing proposed 18th ed changes, the IET agreed with you
"This means that electrical installers will need to find alternative solutions to provide a power supply to equipment that is required to be on a non-RCD protected circuit, such as switch fused connection units."
Presumably armoured cable, or cable in metal conduit, would prevent the nail-through-cable risk? Or a surface run T&E cable where the cable is obvious. And then the RCD can be on the end of that cable to protect the appliance.
For example, an MCB feeding a single run of surface T&E going to three RCD sockets. If an appliance fails, its socket RCD trips. It doesn't trip the other two appliances. You would obviously test the RCDs at the time of installation in the usual way.
That would mean every appliance is RCD protected, and the risks to the cable are managed. IANA electrician but would that meet the regs?
Although three RCBOs in the CU would probably be neater, if the wiring is manageable.
Install a couple of dedicated radial circuits - one for the comms cabinet, and one for the refrigeration sockets. Each with its own RCBO. Chances of getting a RCD trip on a fridge is small, so they can share one circuit. No additional hoops to jump through.
I fitted a non-RCD spur to feed my computer room, socket in the airing cubboard used to light the loft (don't want to be plunged into darkness while up there) and the fridge. That was before (cough) Part Pisstake and the RCD I fitted for the 2 ring mains has never tripped. In fact the first time it tripped was when I bought that Schneider test plug when it tripped immediately. How many people have ever lost freezer contents because an RCD has tripped ?. In my experience Beko fridges are quite capable of ruining your frozen food without any 'help' from an RCD.
We did - quite a lot of value in the food we lost. That was due to our house RCD tripping during a thunderstorm, because of the circuit which went to an outbuilding. Nothing was plugged in there, but we found empirically that if the circuit was powered-up, the RCD would trip in a storm, whereas if it wasn't, the RCD was fine. We got into the habit of turning off its MCB if we were going away on holiday; if it happened when we were at home, it was easy for us to reset the RCD.
Our trusty Beko in the garage finally packed up after about 10 years service. Luckily I happened to check it (as I do sometimes when I go into the garage) not too long after it had apparently happened, because most of the food was semi-frozen. All we lost was some ice-cream. The rest of the food was hard enough that we decided it was safe to cook and re-freeze: our Aga had a lot of use that day and there was a very appetising smell of cooking coming out of the chimney all day ;-) In that case, there was an open circuit on the motor or thermostat. The wires were fine up to the last point that I could test, beyond which was a sealed unit. It's still waiting in the garage for the local council to collect, but because that service costs money and they will take (I think) 3 items for the price, we'll wait until we have another two items so we get our moneysworth ;-)
When the freezer that came with the house (left by the previous occupants sold to us) packed up, we bought a Beko to replace it. It lasted about 4 months before it failed: we noticed because we have energy-monitoring plugs on that freezer and on the one in the garage, to look for anomalous usage such as "doesn't come on any more". I looked at the plug one day and saw a different failure mode: the freezer had been on permanently instead of cycling on and off according to the thermostat. Beko support were inept and took ages to send out an engineer (*). The first engineer diagnosed a faulty circuit board, but when the second engineer came to fit it, he diagnosed lack of refrigerant and he examined the inside (which the first man hadn't) and found signs of "coolant burn" on a pipe so the leakage was evidently near there. The freezer was replaced under warranty and so far had behaved perfectly. If I'd have been Beko I'd have wanted to examine the freezer to find out *how* the coolant hand leaked out - was there a manufacturing or quality inspection problem? But they just sent someone to take it to the local tip.
(*) They didn't send their own engineers but sub-contracted to local third-party firms. The first time they made a "confirmed booking" they referred the job to a company that covered the wrong area, who bounced the call back to Beko - but no-one told us or had the gumption to re-book with the correct company. When I rang to find out what had happened, they made another booking, but did so unilaterally without checking that the date they proposed was one that the (correct) third-party company could manage. Like I say, inept. I made a real nuisance of myself, copying emails to managing directors to make sure that people high-up were aware of the problem so something could be done about preventing it happened again. Beko probably make good products (apart from the one whose coolant leaked out, which was a "lemon") but their support department needs a kick up the arse.
Are you sure this is necessary or are you trying to solve a problem you don't have? I was advised once to avoid RCDs to avoid nuisance trips, but I over-ruled the electrician.
The only trips I have had were with the old washing machine at the start of the spin cycle, which I blamed on the washing machine and on a couple of occasions when lightbulbs failed with a loud bang, which were appropriate trips.
I now have RCBOs on every circuit and I think there has been one trip
- genuine leakage to earth. At least RCBOs limit the outage to one area. My PC is on its own radial socket with its own RCBO.
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